
A METHOD 



FOR THE 



ANALYSIS OF MILK. 



E. II. VON BAUMIIAUER. 



TRANSLATED BY H. CATUUNGTON BOLT 



sprinted from Me American Chemist, November, 181 



NEW YORK: 

JOHN F. TROW & SON, PRINTERS, 

205-213 East 13th St. 



A METHOD 



FOR THE 



ANALYSIS OF MILK. 



BY 




E. II. YON BAUMHAUEfl. 

TRANSLATED BY H. CARRINGTON BOLTON, PH.D. 



Reprinted from the American Chemist, November, 1876. 



NEW YORK : 
JOHN F. TROW & SON, PRINTERS, 

205-213 East 12th St. 






c 



cv 



1 



■?* 



(o 
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A METHOD FOR THE ANALYSIS 
OF MILK.* 

(Bead at the Buffalo Meeting of the American Association for the 
Advancement of Science.) 

Translated for the Author, by II. Carrington 

Bolton, Ph.D. 
About ten years ago I published the results of a long 
series of researches on the composition of cow's milk 
in the Netherlands, the examination being extended 
not only to milk in its pure state, as yielded by the 
cow whether stabled in winter or in the pasture dur- 
ing the summer, but also of the milk furnished to the 
inhabitants of our large cities. This investigation 
proved that the only adulteration to which milk is 
subjected in the Netherlands consists in skimming and 
dilution with water ; but this fraud is sometimes prac- 
tised on so large a scale that more than half the milk 
sold is mixed with water, and in order to conceal the 
blue color produced by diluting milk frequent use 
was made (in Amsterdam, at least) of water of a dirty 
yellow hue. 

In connection with these investigations, which em- 
braced more than 150 different samples of milk, I de- 
vised a new method for the determination of the 
essential constituents of this liquid, which will be 
found advantageous both on account of the accuracy 
of the results and the rapidity of the execution, and 
is especially commended to chemists who are called 
upon to testify as experts in legal processes, and to 
those who have a large number of analyses to make. 



* Dr. Von Baumhauer stated, during the discussion which followed 
the reading of this paper, " that each milk inspector in Holland ia 
furnished with a lactometer."— Tbanslator. 



Since the chief alteration to which milk is submitted 
consists in removing the cream and adding water, it 
has been supposed that the determination of the pro- 
portion of cream by means of the creamometer or the 
lactoscope, combined with a determination of the 
density by means of a hydrometer, sufficed to decide 
with certainty not only whether the milk had been 
sophisticated, but also to what degree the skimming 
and dilution had been practised. As to the determi- 
nation of the specific gravity alone, notwithstanding 
that in certain countries this is the method of testing 
exclusively employed by the police, it is evident that we 
cannot learn much from it, since milk is a solution of 
substances specifically heavier than water, in which are 
suspended globules of cream specifically lighter than 
water; whence it of necessity follows that milk 
skimmed and diluted with water may have the same 
density as milk rich in cream and free from admixture 
of water. 

In the task before me, I endeavored to settle these 
three points : 

1st. Is the hydrometer fitted to give the density of 
milk with accuracy ? 

2d. Does the estimation of the density of skimmed 
milk make known the quantity of dissolved matter ? 

3d. Do the creamometer and the lactoscope indicate 
with accuracy the proportion of the fatty globules 
held in suspension ? 

In studying the first point I naturally had in view 
all the hydrometers of constant weight, without regard 
to the names they bear or the graduation with which 
they are provided. I have already stated that consid- 
ered by themselves, and without a simultaneous deter- 
mination of the proportion of the cream, the hydrome- 
ters do not give us much information as to the nature 
of fresh milk ; but we must study to see if there are not 
still weightier reasons for regarding the use of hydrom- 
eters for milk as disadvantageous. 



In the first place the coefficient of dilatation of milk 
is unknown ; the tables which have been constructed 
in accordance with the experiments of certain observers, 
do not merit our confidence, from the fact that the 
ratio of the soluble matters varies greatly in different 
samples of milk. We are obliged, therefore, in using 
the hydrometer, to work invariably at one and the 
same temperature. 

There is another circumstance which may cause the 
hydrometer to give very unreliable indications, espe- 
cially if minute precautions are neglected. When a 
hydrometer is immersed in a liquid, and allowed to 
move freely, it sinks to a greater depth than that at 
which it will come to rest after a few oscillations, and 
at which its reading would be taken ; this depth is 
moreover greater in proportion to the height above the 
point of equilibrium at which the instrument is let 
fall. 

Therefore, since milk is a liquid more or less viscid, 
it is easy to see that the stem of the hydrometer being 
moistened by the milk retains a considerable quantity 
adhering to it, which renders the weight of the instru- 
ment very variable. Experiments which I have made 
in this connection show that very serious errors may 
result, sufficiently great to be equivalent to a differ- 
ence of five per cent, more or less of water in the milk. 
It is moreover evident that these errors are greater the 
smaller the bulk of the hydrometer relatively to the 
diameter of the stem, so that with the small galacto- 
meter of A. Chevallier, which is so highly praised by 
Messrs. A. Chevallier and O. Reveil,* the errors would 
be larger than with the lactometers of large size gener- 
ally used in this country [i.e., in Holland]. 

By making comparative determinations of the den- 
sity of different samples of milk by means of direct 
weighings, and by the use of either Che vail ier's galac- 

* Notice sur le lait. Paris, 1856. 



6 

tometer or of Geisler's hydrometer (which has a vol- 
ume of about 50 c.c. and a stem measuring scarcely 3 
mm. in diameter), I satisfied myself that the indica- 
tions of these two instruments agreed very imperfectly 
with the results obtained by the first- named method. 
This applies to skimmed milk, and to a greater degree 
to fresh milk ; for the latter there is still another cause 
of error. Milk is actually a liquid heavier than water, 
in which lighter globules float with a tendency to come 
to the surface. We have then a case similar to that of 
a viscid liquid holding in confinement air-bubbles, 
which, by attaching themselves to the lower surface of 
the immersed bod}% necessarily vitiates to a certain 
extent the determination of the density. We will see 
presently that this error becomes much greater in the 
case of milk which has been violently agitated. 

I found also that even in the case of skimmed milk, 
the specific gravity, though determined with great care, 
bears no fixed relation to the sum of the constituents 
held in solution; while as to fresh milk, that goes 
without saying. The density of the skimmed milk 
does not indicate the sum of substances held in solu- 
tion, because the relative proportion of sugar, casein, 
extractive matter, and inorganic salts is not the same 
in different samples of milk. 

Experiments have also shown that very little con- 
nection exists between the indications of the cream- 
ometer and the lactoscope, and the quantity of fatty 
matter contained in the milk which can be extracted 
by ether. It is moreover natural that this should be 
the case, especially as we have to deal with milk sent 
from a great distance and which has in consequence 
been subjected for a greater or shorter period to all 
kinds of vibrations and shocks. 

Before going any further we must consider for a 
moment the churning of milk, in order to combat a 
common error with reference to what takes place in 
this operation. Most farmers think that butter sepa- 



rates on churning only when the milk becomes acid ; 
science teaches us, on the contrary, that sweet milk 
yields butter by churning as well as sour. It is also 
supposed that during the agitation of the milk with 
the air, the milk becomes sour, and the lactic acid 
found dissolves the membranous envelope of the milk 
globules, the contents of which are then free to collect 
as little lumps of butter. The following experiments 
show beyond a doubt that these views are incorrect, 

The milk used in these experiments was drawn in 
the morning at half- past four o'clock, on a pasture in 
the neighborhood of Amsterdam, and the precaution 
was taken of holding the pail close up to the udder, 
in order to avoid as much as possible the formation of 
froth ; this milk was brought in two pails into the 
laboratory, care being given to avoid agitation. 

The milk had a neutral reaction, at least during the 
first seconds of the contact with test-paper ; later the 
reaction was acid.* 

We took several flasks, each having a capacity of 
two litres, and into each we poured one litre of milk. 
To one of these flasks we added several drops of lactic 
acid, so that the milk reacted acid at once. To the 
second flask no addition was made. To the third, 
several drops of a solution of potassium carbonate 
were added, until the milk had a weak alkaline reac- 
tion; in a short time, however, the reaction became 
acid, and immediately after churning it was neutral. 
Into a fourth flask we introduced a much larger quan- 
tity of potassium carbonate, such an amount that the 
milk remained alkaline after churning. The milk had 
a temperature of 21° C. These four flasks were shaken 



* I think that for the examination of milk as to its action on test- 
paper, it is absolutely necessary to take into consideration the reaction 
which is observed in the very first moments, since it is well known that 
milk exposed in thin layers to air sours rapidly. It is probable that 
the widely differing reports of different observers of the reaction of 
milk should be attributed to this circumstance. B. H. von B. 



8 

by four persons with the same force, for one minute, 
and then allowed to rest. On the sides of each flask 
we saw granulations, a proof that the butter had begun 
to separate. Examined under the microscope these 
particles appeared like large fatty drops, of an irregu- 
lar oval form, frequently like a mulberry in shape, 
and these drops flattened by pressure between two 
plates of glass. The flasks were shaken a minute 
longer. The particles deposited on the walls had in- 
creased to an equal extent, and the same took place 
each time the shaking was repeated. After ten min- 
utes the particles had become of considerable size, and 
after eighteen minutes we found in each of the four 
flasks little buttery masses of a yellow color and the 
size of a pea ; the separation of the butter, both as 
regards its quality and its quantity, took place in a 
very satisfactory manner. After the operation, as 
already stated, the milk had a neutral reaction in the 
third flask and an alkaline reaction in the fourth. No 
difference whatever was noticeable in the four flasks. 
The butter taken out of the flasks and examined under 
the microscope presented precisely the same aspect as 
that of the particles formed after the first minute's 
shaking. 

In the milk deprived of the fatty matter, very small 
globules were seen in abundance, but the number of 
large globules had diminished considerably. 

This experiment, which any one may repeat for him- 
self, proves, as I think, that we must abandon the idea 
of a solution of the envelope of globules by means of 
the lactic acid formed, and strikes a blow at the. very 
existence of these membranous envelopes of the fat- 
globules, the belief in which rests moreover on a very 
weak foundation. 

The idea which I entertain of churning is as follows : 
By agitation the milk globules are thrown against 
each other with a certain force, and when the tempera- 
ture is suitable, they remain adhering to each other, 







and this gives rise to the mulberry-shaped lumps which 
compose the yellow butter desired. When the milk is 
too cold, every farmer knows that he can churn for 
hours without separating the butter, and hence he 
adds a little warm water. In this case the globules of 
the milk are too hard, even crystalline, and the ag- 
gregation cannot take place. On the other hand, what 
ensues when the milk is too warm, as happens in sum- 
mer, or in winter after too much warm water has been 
added ? 

The butter is then burnt, as the farmers say ; it forms 
small particles, does not easily collect in lumps, and 
yields a white mass, opaque, very soft, and which by 
exposure to cold becomes harder, but does not become 
yellow and translucent. This is because the fatty 
matter has been melted ; the little drops unite to form 
larger drops, but they cannot yield lumps, because in 
the existing conditions churning produces an emul- 
sion. In spite of all their efforts, it happens that the 
farmers do not succeed with the churning, and they 
attribute their want of success to all sorts of causes. 
The use of the thermometer would teach them to avoid 
these accidents. The temperature at which tine butter 
is obtained is fixed between very narrow limits; 
numerous experiments, in which I also used churns, 
have established this temperature between 20° and 
22° C. By always working at this temperature, in- 
stead of adding warm water or cold water almost 
without care, the butter-maker will avoid many 
failures. 

Besides the experiments just described I made two 
others : I took two flasks containing milk ; to one I 
added sodium sulphate, and to the other sodium chlor- 
ide in such quantity, that after shaking a moment 
some of the salt remained undissolved. After the 
milk, which had cooled down considerably, was 
brought to the temperature of 21° C, the two flasks 
were shaken as before during a specified number of 
1* 



10 



minutes ; I found thus that the addition of the salts 
had no sensible influence on the separation of the 
butter. 

A final experiment will show us clearly why the in- 
dications of the creamometer are of no value after the 
milk has been shaken, and why in consequence this 
instrument can be of no use in large cities where the 
milk is often transported several miles in wagons. 

Creamometer No. 1 was filled with milk not shaken ; 
No. 2, with milk which had been agitated one minute ; 
No. 3, with milk which had been agitated two minutes, 
and so on. In the creamometers which contained 
milk agitated for a few minutes only, there formed 
after a short time a well defined layer of cream, 
which occupied 1 to 2 hundredths of the volume of 
the milk taken, and beneath this a second layer 
formed over night, having an entirely different aspect 
from the first layer. On the other hand, the milk 
which had been shaken ten minutes or more yielded, 
as soon as poured into the creamometers, small lumps 
which came to the surface, and occupied in one 2 to 
3, in the other 11 to 12 hundredths of the capacity. 
In all the creamometers a second layer of cream 
formed on standing, and the longer the milk had 
been shaken the smaller was this layer. The indica- 
tions of the creamometers were naturally very discord- 
ant, while that containing the milk not agitated 
marked 8 J, the other samples marked between 10 and 6. 

From the foregoing it is evident in my opinion that 
a simple determination of the density of milk and of 
the amount of cream, by means of the creamometer 
or of the galactoscope, by no means enables us to judge 
with any degree of certainty of the amount of the 
sophistication, whether by skimming or by adding 
water. Such determinations can at best be used only 
for ascertaining an addition of water equivalent to 10, 
20, 30, or 40 per cent., and a considerable removal of 
the cream : and in certain cases when the water em- 



11 

ployed to adulterate the milk is brackish, as is the 
case in Amsterdam, a knowledge of the density en- 
lightens us still less on the composition of the liquid. 

The principal reason which prevents recourse to 
complete analysis for determining the adulteration of 
milk lies in the circumstance that these analyses, to be 
of any service, require to be made in large numbers, 
and each requires much time and labor. The idea has, 
therefore, occurred to various chemists that it may 
suffice to estimate one of the constituents of the milk 
in a rapid and yet accurate manner, and to calculate 
from this determination the degree of sophistication 
to which the milk has been submitted. 

Thus M. Marchand has constructed a lactobutyro- 
meter, in which a given volume of milk mixed with a 
small quantity of a solution^ of sodium hydrate is 
agitated with an equal volume of ether, after which the 
same amount of alcohol is added,"the vdiole is. shaken 
again and gently warmed. The butter, he claims, is 
completely insoluble in this mixture, and collects on 
the surface in a layer the thickness of which can be 
read on the graduated tube. 

Messrs. Re veil and Chevallier, starting with the idea 
that the proportion of lactose is sufficiently constant 
in milk, heat the milk to incipient ebullition, and add 
(as suggested by C. Struckman, Chem. Pharm. Gentral- 
blatt, 1855, p. 695) a few drops of acetic acid, thereby 
obtaining as they claim, and as confirmed by Mr. ter 
Kuile, a solution as limpid as water, in which the 
lactose is determined by Barreswil's method. I must 
say that I have tried this process many times, and al- 
though I have varied the quantity of acid added, and 
have tried acids of different kinds (acetic, sulphuric, 
hydrochloric, oxaHc, tartaric), I have never succeeded 
in obtaining a limpid liquid. 

Usually it is very turbid ; in the most favorable cases 
it remained opalescent, but to such a degree that it 



12 



was impossible to estimate the sugar either by the 
copper solution or by the polariscope. 

L. Lade * recommends the estimation of the propor- 
tion of casein by means of a standard solution of 
mercurous nitrate ; E. Monier f suggests the use of a 
standard solution of potassium permanganate for the 
same purpose. 

But the question arises, is it possible to decide, from 
the estimation of one of the constituents of milk, 
what alterations this liquid has suffered? All ex- 
perimenters have found the richness of milk in butter 
is very variable, even for the same cow, and the same 
may be said to obtain to a less degree of the substances 
dissolved in the milk. 

The relative proportion of lactose and of casein 
shows marked variations in different samples of milk, 
as demonstrated by my investigations. 

Judgment should not then be founded upon estima- 
tions of a single essential constituent of milk, but 
upon the estimations of several constituents. For the 
same reason, I also disapprove of employing exclu- 
sively the determination of the non- volatile substances 
in the milk, contrary to the opinion of many chemists, 
who see in this method a sure means of determining 
the dilution by water. 

At the same time I consider this determination, com- 
bined with that of the fatty matter, and also (in 
doubtful cases) with that of the sugar and casein, as 
the only good method of testing milk. 

Up to the present time, however, the estimation of 
the non- volatile constituents of milk has always been 
a very long operation, and accompanied with many 
difficulties, so that it was impossible to make a number 
of these determinations in a short time with the neces- 

* Schweiz. Zeitschrift filr Pharmacie, reproduced in the Polyt. 
Centralblatt, 1852, 2d Sec. 

t Comptes rendus, 1858, xlvi., p. 256, Journ. f, prakt, Chemie, 
1858, p. 478. 



13 

sary accuracy. I believe that the method I am about 
to explain will effect a notable improvement in this 
respect. 

It is well known that during the evaporation of 
milk (even when at a temperature below boiling, as 
on a water-bath), there forms on the surface a very 
firm pellicle, which prevents further evaporation; 
when this film is removed, a new one forms immedi- 
ately, and so on. 

This film is composed of casein penetrated with 
fatty matter. By constantly stirring and breaking the 
pellicles as fast as they form, it is possible to evapo- 
rate the milk to dryness, or rather apparently so, for 
the residue is not yet by any means free from water, 
and must then be dried at a temperature higher than 
100° C. Most chemists advise using a temperature of 
105° C. ; if, however, it is desired to continue the desic- 
cation until two successive weighings (each after dry- 
ing one hour at 105° C.) show no loss, the residue is 
found to become colored of a dark brown, particu- 
larly at the edges, and it is almost impossible to obtain 
two equal weights on account of the great hygro- 
snopicity of the brown substance formed (probably 
caramel). Dissolved in water, the residue yields a 
brown solution. It is evident, then, that the weight of 
the residue thus obtained does not express the sum of 
the solid constituents of the milk. 

The method described by Mr. Haidlen, and which 
consists in adding to the milk to be dried one-fifth its 
weight of gypsum dried at 100° C, has indeed some- 
what lessened the inconvenience named, but has not 
entirely removed it, and besides does not dispense 
with incessant agitation of the liquid during the whole 
duration of the evaporation— during, in fact, several 
hours. 

Moreover, this method may occasionally give rise 
to serious errors, when the gypsum is not perfectly 
pure, or when it has not been dried with sufficient 



14 



care. If dried at too high a temperature, gypsum 
changes into anhydrite, which takes up water of crys- 
tallization as soon as it comes in contact with moisture. 
On this account Mr. Wicke .has recommended the sub- 
stitution of sulphate of barium for gypsum ; the 
barytes, having been heated to redness and thus de- 
prived of all traces of water, can be moistened and 
dried at 105° without changing in weight. 

Instead of these two substances, C. Brunner* pro- 
poses the use of wood charcoal in coarse powder ; but 
I must protest strongly against employing this mate- 
rial, since wood charcoal, as is well known, cannot be 
considered as a body indifferent in its behavior to 
organic substances. 

All things considered, the best material to mix with 
the milk to facilitate evaporation is incontestably pure 
sand washed with hydrochloric acid, as suggested by 
Otto. 

After having satisfied myself by repeated experi- 
ments that the determination of the fixed constituents 
of milk, by means of any of the foregoing processes, 
not only leaves much to be desired with respect to 
accuracy of the results, but also necessitates far too 
much labor ever to be employed in cases where hun- 
dreds of samples are to be tested. I conjectured that 
the desired ends might be attained by using a per- 
fectly indifferent porous mass capable of absorbing a 
given amount of milk (not too small) without allow- 
ing the smallest loss by dripping from the porous 
material. The substance thus impregnated could be 
exposed to a current of dry air, at first at a moderate 
heat and afterwards at a temperature slightly above 
100° C.f Owing to the extremely divided condition of 
the milk, no films could form to prevent the free pas- 
sage of air through the porous mass after drying. The 



* Polyt. Journ., cxlvii., p. 132. 

t Liebig's Annalen, April, 1857, p. 60. 



15 

increase in weight of this mass would give the sum of 
the fixed constituents of the milk. My first experi- 
ments to realize this idea were unsatisfactory. 

Plaster tempered and solidified absorbed scarcely 
any milk, even when fragments of pumice-stone were 
mixed with it. Pumice-stone itself is too fragile to 
allow of handling it and drying the pieces without a 
small amount of powder becoming detached. Of 
various kinds of earthenware which I tried none were 
sufficiently porous. I then had little cups made with 
very thick sides of porous baked clay; but in this 
case again the porosity was insufficient, the cream re- 
mained in large measure on the surface, and formed 
by drying a layer impenetrable to air. 

The most simple measure is often that one thought 
of last, and this was true in my own case. At length 
I found that sand well washed with hydrochloric acid, 
ignited strongly, and placed in a well-dried filter— not 
supported in a funnel, but freely suspended in such a 
manner that the whole surface of the paper is exposed 
to the air— that sand thus treated was, on account of 
its chemical inertness, the substance which suited best 
the object in view. 

The little difficulties which were met with in prac- 
tice were easily overcome, and I believe I can affirm 
that the method I devised for the analysis of milk is 
capable of extended application in chemistry, especi- 
ally in physiological chemistry. In the latter branch 
of the science, difficulties of every kind oppose them- 
selves when it is required to evaporate to dryness 
solutions of animal and vegetable substances ; as, for 
instance, in the analysis of blood, of bile, of urine, 

etc. 

Select sand which is quite white and clean ; better 
yet would be colorless quartz in powder. Digest the 
sand with hydrochloric acid, wash well with rain- 
water at first and lastly with distilled water, until the 
latter yields no trace of acid. This may be prepared 



16 



on a large scale. Dry the sand, and ignite in a clean- 
covered Hessian crucible, and while still red hot pour 
the contents from a certain height upon a clean stone 
in order that the organic matter carbonized during the 
ignition may be burned while falling through the air. 
After cooling, place the sand in clean bottles pre- 
viously dried, and cork well ; thus the sand may be 
preserved for use. 

The filter paper, cut in discs of 10 to 12 cm. in 
diameter, is also washed with hydrochloric acid and 
water, then dried in a current of dry air, raising the 
temperature at last to 110° C, and finally preserved in 
wide-mouthed bottles closed with rubber corks. 

A disc of copper standing on feet 10 cm. in height 
(see Fig. 1) is pierced with ten, twelve, or a larger 
number of round holes having a diameter of 5 cm., 
and placed at a certain distance from each other. In 
these holes are hung rings made of glass rods, the di- 
ameter of the rings being 4 cm., and that of the rods 
3 mm. ; these rings rest on the copper disc by mean 
of little curved arms of glass soldered to them. 

Subsequently I employed rings made of baked clay. 
Iu each of these rings is placed a filter folded in 
quarters in the usual manner, and filled with sand up 
to i cm. of the edge: this step requires only a few 
minutes. Near each hole a number is scratched upon 
the copper disc ; in the centre of the disc a wooden 
handle is fastened, by means of which the disc, with 
its load of sand-filled filters, can be handled with ease ; 
the disc also has a small hole near the circumference, 
through which a thermometer is introduced. 

The heating apparatus consists of a copper bath 
with double walls, between which is placed paraffin ; 
in this air-bath one or two copper discs above de- 
scribed, and which I call supports, are inserted one 
above the other, as shown in the cut ; A and B have 
each ten holes, so that twenty filters can be dried at 
one operation. 



17 



The cover of the bath fits closely, and carries at its 
centre a small tube, which is covered about with wood 




and serves at the same time as a handle ; this tube is 
connected with a Woulfe-bottle C, in which the water- 
gas condenses, and which is joined to a strong aspira- 
tor, such as I have described in the Archives JSfeerland- 
vol. i., p. 191. 



18 



The cover is pierced with another opening, in which 
is fastened a thermometer ; the bulb of this thermom- 
eter, passing through the holes in the supports, reaches 
to a level with the points of the lower filters. Between 
the double walls of the bath is fastened a copper tube, 
bent twice at right angles, and terminating at one end 
in the middle of the air-bath, while the other end is 
connected, at the close of the operation, with aii appa- 
ratus for drying the air over sulphuric acid or calcium 
chloride. 

As many glass flasks and funnels are required as 
there are analyses to be executed ; the capacity of each 
flask is exactly 100 c.c, as indicated by marks on the 
necks ; the funnels (Fig. 2) have their edges ground 



Ti 9 M 




with emery and are covered with watch-glasses. 
All are carefully numbered. The funnels are of such 
a size that the filters hang freely when placed on the 
rings of glass, and after covering the funnels a space 
of \ cm. remains between the upper edge of the filter 
and the glass cover ; to the stem of each funnel is at- 
tached a caoutchouc tube, closed with a spring-clamp. 
Finally, as many desiccators are required as there are 



19 



analyses to be made, for it is not safe to use a common 
desiccator for substances as hygroscopic as the fixed 
solids in milk. I use as a desiccator or receiver a bea- 
ker glass, in which is placed a triangle for support- 
ing the rings with their curved arms above described. 
At the bottom of the glass is placed calcium chloride, 
and the whole is covered and closed with a hood of 
india-rubber. 

The milk analysis is conducted as follows : Having 
filled the filters with sand, place them on the support 
and heat them for half an hour in the air-bath at 1 1 0° C. ; 
after cooling them in the desiccators, weigh them, suc- 
cessively placing them on a small beaker glass, from 
which the bottom has been cut and the edges of which 
have been ground (Fig. 3). 



saM Fi 3 m 




In my experiments the beaker glasses with glass rings 
and sand-filled filters weighed from 68 to 75 grammes. 
Having completed the weighings, take 10 c.c. of milk 
with a pipette from each of the samples, the tempera- 
ture of which has previously been brought to 15° C, 
and add the milk to one of the filters, taking care to 
moisten the whole surface of the sand, save the exte- 
rior edge. 

The sand on the filter can absorb more than 10 c.c. 
of milk without the point of the filter becoming 
moistened ; on some occasions a few drops of liquid 



20 



ran from the point of a filter, but this was when I had 
to deal with milk adulterated with an equal volume of 
water. In case this happens, the filter is replaced by 
another, to which only 5 c.c. of milk are added ; then, 
after the filters are nearly dry, the other 5 c.c. are added 
and the desiccation continued. In making analyses, I 
continually worked with 10 c.c. of milk, and I calcu- 
lated the results as parts in a thousand by volume — 
that is to say, in a litre. I think this method of pro- 
cedure is more rational than to give the composition in 
hundred parts by weight, when we consider that milk 
is sold by measure, and not by weight. 

When all the filters have been charged with milk, 
the support is placed in the air-bath and the tempera- 
ture is raised to about 60° or 70° C, which heat is 
maintained so long as the current of air which passes 
through the apparatus deposits moisture in the Woulfe- 
bottle. After this the aspiration is moderated, and air 
previously dried is passed through the apparatus, which 
is then heated to 105° C. for a good half -hour. The 
desiccation is entirely completed in 4 to 5 hours, with- 
out the necessity of giving it any attention, save to ex- 
amine from time to time the stand of the thermometer. 
The filters are then allowed to cool one hour in the 
receivers, and weighed again. The difference be- 
tween the first and second weighings gives the sum of 
the fixed constituents of the milk. For greater pre- 
caution, the support may be replaced in the air-bath 
and heated an hour longer at 105° C, again cooled and 
weighed, in order to make sure of complete desicca- 
tion ; but if the process described has been followed 
closely, it will always be found that the second weigh- 
ing differs from the first by only 1 (or at most 2) mil- 
ligrammes, more or less. Care must be taken not to re- 
move the filters too soon from the receivers, since sand 
cools very slowly. 

It is also of the greatest importance to avoid a 
higher temperature than 70° C. during the evaporation 



21 

and before the filters are dry, since if wet filters are 
heated suddenly to 100° C, their edges become imme- 
diately of a brownish yellow color ; but by effecting 
the drying at a low temperature this does not occur. 
When the mass is once dry, it sustains a heat of 105° 
C. without browning. Otto has pointed out this fact 
previously. 

As an example, I produce the results of an exami- 
nation of asses' milk, collected in a stable at Amster- 
dam, and analyzed for the purpose of testing the ac- 
curacy of the method. 

Three sand-filters, dried, weighed : 

No. 1 74.883 grammes. 

No. 2 71.577 " 

No. 3 71.338 " 

Each was charged with 10 c.c. of milk, and dried, 
and weighed again ; this gave • 

No. 1 75.9S1, and consequently 1.098 fixed solids. 

No. 2.... 72. 672, " ' ; 1.095 " « 

No. 3 72.438, " " 1.100 " 

After drying the filters an hour longer in the air 
bath and cooling, the following figures were obtained : 

No. 1 75.980 grms. 

No. 2 72.672 " 

No. 3 72.438 " 

It is evident that the second drying was not neces- 
sary. 

To determine the proportion of fat, we proceed as 
follows : The filters with contents are placed in the 
funnels, which are filled with anhydrous ether and 
closed for half an hour ; the ether is then drawn off 
by opening the pinch-cocks, and the operation repeated 
twice ; the filters are washed twice more with ether and 
placed on the support, which is then introduced into 
the air-bath. Each filter requires scarcely 100 c.c. of 
ether. If the desiccation has been carefully made the 
ether runs off as colorless and as limpid as water. 



Nos. 1 and 2 were thus treated, then dried and 
cooled as before ; this requires very little time. The 
weighings gave : 

No. 1 . . .75.775 grms., or a loss of 0.206 
No. 2... 72.460 " " " 0.212 

The filters were washed again with 100 c.c. of ether 
to each, dried, cooled, and weighed again ; this gave : 

No. 1 75.775 grms. 

No. 2 72.460 " 

The first treatment with ether had dissolved all the 
fat. 

Some chemists recommend to evaporate the ethereal 
solution in weighed capsules, to dry the residue at 
100° C, and to weigh it. I do not advise this method, 
partly because a loss results by the ethereal solutions 
creeping over the sides of the capsules, and partly 
because I have found that fat dried in this manner at 
100° C. partially evaporates, as is shown by the odor 
and the rise of white vapors. 

For the determination of the sugar we proceed in 
the same manner as with the fat, substituting, however, 
warm water for ether ; the water which filters through 
as collected in the 100 c.c. flasks above mentioned. 
By using 90 c.c. of water in successive portions the 
sugar is completely extracted. Since, however, casein 
is not entirely insoluble in cold and hot water, the fil- 
ters lose weight by a second treatment with warm 
water ; the second filtrate does not contain sugar, ac- 
cording to my experiments. 

Nos. 1 and 2 treated in this way, dried and cooled, 
gave on weighing 

No. 1 75.035 grms., or a loss of .740 

No. 2.... 71. 730 " " " .730 

After being again treated with 100 c.c. of warm 
water, dried and cooled : 

No. 1 .. .75.011 grms., or a loss of 0.764 
No. 2.,, 71. 714 " " « 0.746 






By "a third treatment we obtained : 

No. 1 . . . 75.004 grms., or a loss of 0.771 
No. 2... 71. 700 " " " 0.760 

When the desiccation has been property conducted, 
the water solutions are quite colorless and clear. 

The aqueous solution first obtained was cooled to 
15° C. in the graduated flask in which it was collected, 
diluted to 100° C, and in this the sugar was estimated 
by means of Mulder's standard solution. 

10 c.c. of the test solution, diluted with 10 c.c. of 
water, required : 

No. 1 . . .5.25 and 5.30 of sugar solution. 
No. 2... 5.35 " 5.30 

The second filtrate obtained above was added to 5 
c.c. of the standard solution, and on first boiling no 
reduction took place ; but by continuing the ebullition 
a very slight one ensued — so weak, however, that after 
adding all the filtrates of the first and second treat- 
ment, making 400 c.c. in all, the liquid remained of a 
dark blue color. The reduction observed may be 
ascribed to the casein, which by prolonged boiling re- 
duces a small quantity of the copper solution. 

A. creamometric determination of the asses 1 milk 
was also made, giving 3 per cent, by volume. The 
galactometer marked 110 on the yellow scale in the 
milk in its natural state, and 107 on the blue scale 
after skimming. 

As in all my analyses, I also estimated the ashes of 
the milk, by placing 10 c.c. of milk in a platinum 
crucible, adding several drops of acetic acid (to pre- 
vent the formation of films and to hasten the evapora- 
tion), and evaporating on the water-bath, igniting to 
a white heat, and weighing. This gave 0.0355 grms. 
of ashes. 

The analysis of asses' milk, which I have merely 
taken as an example in order to show the accuracy of 
the method, yields the following figures in a litre ; 



24 



Fat 20.9 grammes. 

Milk sugar 61.5 " 

Other substances soluble in water. 12.0 " 
Substances insoluble in water. ... 15.3 " 

Mineral matter 3.5 " 

Since milk is a mixture of various non-volatile 
substances and water, and no constant proportion by 
weight exists between the constituents, the only way 
to determine its average composition is by the analysis 
of a large number of samples of pure milk, collected 
from different localities and from animals placed in 
varying conditions and submitted to different nourish- 
ment. 

In my memoir, Over de hearing der Tcoemelk en 
over de melh in Nederland* I published the composi- 
tion of a large number of specimens of cows' milk 
received from different parts of the country, and 
which represented not only milk in a state of purity, 
but also milk as delivered to the inhabitants of cities. 
In Table I., I have collected the twenty samples 
which were sent to me as coming direct from the cow, 
though I cannot affirm that they express the exact 
composition of veritable milk, since I do not know 
whether the whole of the milk was drawn from the 
cows' bags ; for it is well known that the milk drawn 
towards the last is richer in butter than that obtained 
at the beginning. 

These twenty samples are of winter milk, and are 
consequently derived from animals fed in stables. 
The following particulars were given me with regard 
to some of them : 

No. 1. — Milk of a cow which had calved three 
weeks previously, and fed on hay and linseed cake. 

No. 3. — Milk of a cow which had calved four 
times, the last time January 17th (three weeks previ- 
ous to the analysis of the milk). Food : hay, linseed 
cakes, and carrots. 

* Verslagen en Mededeelingen der Koninklijke Akademie der 
Wetenschappen, Section des Sciences phys., t. viii., p. 145. 



25 



Galacto- Cream- 
meter, ometer. 




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16.3 17.0 
15.2 15.6 
16.7 17.5 
14.7 15.2 

14.4 — 
15.0 16.0 

14.5 15.6 


i 


01 

a £ • 

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1.0343 1 
1.0320 1 
1.0353 1 
1.0310 1 
1.0303 
1.0319 ] 
1.0307 1 
1.0338 1 
1.0309 1 
1.0280 1 
1.0318 ] 
1.0335 3 
1.0307 
1.0341 
1.0326 
1.0321 
1.0303 
1.0300 
1.0301 
1.0318 


On 100 Parts by Weight 

of Non-volatile Matter 

Deprived of Fat. 


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45.8 12.0 

47.0 11.6 

39.1 14.4 

47.4 11.3 

35.5 20.3 

40.9 14.9 
45.5 12.0 

52.8 
59.3 
52.0 
54.8 
51.1 
51.3 
60.7 
57.8 
59.4 

41.4 19.5 

39.5 16.3 
40.9 20.8 
43.0 20.3 


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123.8 
111.4 
133.6 
108.4 
123.9 
121.6 
112.1 
1-25.5 
110.4 
105.0 
124.9 
12'5.6 
107.1 
137.4 
125.S 
104.4 
112.6 
116.4 
118.8 
122.4 

118.5 




near Amsterdam. 
near Leyden. . . . 
, near the Hague 
it Papendrecht. . 
at Dubbeldam. . . 

ear Utrecht 

ear Utrecht 

near Arnhem. . . 

near Tiel 


near Doesburg . . 

near Zutphen. . . 

near Zutphen . . . 

near Nimeguen. 

near Nimeguen . 

near Nimeguen . 
ear Leeuwarden.. 
lear Leeuwarden.. 
rear Leeuwarden.. 
lear Leeuwarden.. 


I 

* 




1. 11 March, 

2. 11 March, 

3. 4 February 

4. 25 March, 

5. 25 March. 

6. 15 April, n 

7. 15 April, n 

8. 9 January 

9. 7 January 


11. 7 January 

12. 9 January. 

13. 9 January 

14. 7 January 

15. 7 January 

16. 7 January 

17. 28 April, i 

18. 28 April, r 

19. 28 April, r 

20. 28 April, i 





26 



No. 6. — Mixture of milk of eight cows, drawn in 
the morning. Food : hay, potato-parings, malt, and 
linseed cakes. 

No. 7. — Mixture of milk of seven cows. Food: 
hay, linseed cake, and carrots. 

No. 8. — Milk of a cow, drawn at noon. Food: 
hay and turnips. 

No. 9. — Milk of a cow milked at 7 a.m. Food 
turnips, chopped straw, and horse-beans. 

No. 10. — Milk drawn at 8 a.m. Food: hay only. 

No. 11. — Mixture of milk of four cows, milked at 
7 a.m. The cows received daily (for all four) 3 kilos 
cakes of rape seed, 6 kilos of black bread, 8 kilos of 
bran and chaff from wheat flour, 12 litres of small 
potatoes, 12 beets, besides hay and straw. 

No. 12. — Milk drawn at 7 a.m. Food: straw, hay, 
turnip-tops, and a warm feed made of potatoes and 
turnips cut in pieces, cooked, and mixed with colza 
cakes. 

No. 13. — Milk drawn at 7 a.m. Food : hay in 
abundance, a little straw, beets and turnips mashed 
and mixed with colza cakes. 

No. 14. — Milk drawn at noon, the time of " mul- 
sion" being at 6 a.m., noon, and 6 p.m. The cow 
had calved five weeks previously. The food con- 
sisted chiefly of hay, turnips, and a few linseed 
cakes ; she received also, however, kitchen refuse, 
such as potato-parings, cabbage-leaves, etc. It is to 
be noticed that the cream would not rise in the 
creamometer. 

No. 15. — Milk drawn at 8 p.m. ; time of "mulsion," 
6-£ a.m., 1 p.m., and 8 p.m. The cow had calved 
four weeks previously. The food consisted of hay, 
carrots, turnips, half a colza cake daily, potato- 
parings and other kitchen refuse, and material from a 
steam distillery of potato brandy. 

No. 16. — Milk drawn at 7 a.m. ; time of " mul- 
sion," 7 A.m., noon, and 6 p.m. The cow had 



27 

calved towards the end of November. The food 
consisted of hay, oats and oat-straw, half a colza 
cake, and beets. 

No. 17. — Evening milk, and No. 18 morning milk 
of the same cow, that one yielding the most milk of 
any in the stable. Food : hay. 

No. 19. — Evening milk, and No. 20 morning milk 
of the same cow, which was regarded as giving the 
best milk ; also fed on hay exclusively. 

To obtain still more certain data on the mean com- 
position of milk, the milk of five cows, forming part 
of a dairy of Onderkerk, near Amsterdam, was 
examined during a period of ten consecutive months, 
from the moment of calving (which took place in 
winter) until the month of October following, when 
they were taken back to the stable. 

The food supplied consisted of hay and linseed 
cakes in the stable, and grass in the pasture. In the 
stable they were milked at 5 a.m. and 4 p.m. ; in the 
pasture, at 3 a.m. and 4 p.m. Care was taken to 
secure the whole supply of the "mulsion." The 
evening milk and morning milk were examined sep- 
arately. 

The five cows of which the milk was studied were : 

A, aged 4 years ; had calved thrice. 

B, " 6 " " four times. 

C, " 41 " " three " 

D, " 4 " " twice. 

E, " 4£ " " three times ; this cow 
fell sick in June, and was replaced by another. 

F, aged 9 years, and which had calved for the 
ninth time in the month of May. 

The second table gives the composition of the first 
milk secreted, the colostrum. During these three or 
four days the cows were milked three times in twen- 
ty-four hours. Table III. embraces the composition 
of the normal milk from the first week succeeding 
birth. 



28 



The low figures for the non-volatile substances in 
the milk of the nine-year-old cow are very striking. 
Table II. 

COLOSTRUM OP THE COW A. 



Date. 


Non-volatile 
substances. 


Fat. 


Ashes. 


10 December, 1858. . . 


2.885 


0.771 


0.123 


tt i 


I tt 


1.810 


0.580 


0.117 


u i 


( (( 


1.398 


0.302 


0.103 


11 ' 


I u 


1.606 


0.564 


0.096 


tt I 


( u 


1.501 


0.435 


0.087 


U t 


I (( 


1.518 


0.507 


0.089 


12 


( (( 


1.472 


0.497 


0.090 


U I 


t tt 


1.491 


0.486 


0.089 


13 ' 


l tt 


1.387 


0.451 


0.082 



COLOSTRUM OP THE COW B. 



8 January, 1859 


2.059 


0.226 


— 


it u tt 


1.461 


0.132 


0.104 


It t< (( 


1.395 


0.185 


0.090 


9 " " 


1.310 


0.127 


0.090 


COLOSTRUM OP TH* 


: cow c. 




14 January, 1859 


2.899 


0.585 


0.098 


it tt t 




2.178 


0.422 


0.100 


It U ( 




1.630 


0.369 


0.090 


15 




1.262 


0.304 


0.089 


it a i 




1.298 


0.352 


0.085 


kt t< t 




1.368 


0.343 


0.084 


16 " ' 




1.259 


0.299 


0.084 


(( t: t 




1.218 


0.257 


0.083 


17 




1.228 


0.259 


0.080 


tt kt t 




1.232 


0.249 


0.080 


COLOSTRUM OP TH] 


a cow d. 




11 March, 1859 


2.370 


0.330 


0.100 


12 " " 


1.428 


0.268 


0.087 


tt tt tt 


1.472 


0.294 


0.080 


13 " " 


1.216 


0.308 


0.080 


14 " 




0.209 


0.329 


0.076 



COLOSTRUM OF THE COW E. 



17 April, 1859 . 

18 " 

tt tt <t 

19 " '• ! 



2.798 


0.280 


1.959 


0.285 


1.818 


0.312 


1.468 


0.444 


1.389 


0.461 



0.106 
0.092 
0.084 
0.080 
0.076 



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